* Rebels say one died in ambush by Gaddafi forces
* Say Gaddafi fighters spread out in desert
* Rebels say NATO bombing Gaddafi positions (Adds some rebels gathering, explosions)
By Michael Georgy
AJDABIYAH, Libya, April 15 (Reuters) - Muammar Gaddafi's forces opened fire on rebels and killed one near the strategic eastern Libyan town of Ajdabiyah on Friday, insurgent fighters said, after their plan for a new counter-assault fizzled out.
A fighter manning an anti-aircraft gun was shot dead and two others were wounded in the attack, a kilometre (around half a mile) from Ajdabiyah's western gate, according to rebels at a checkpoint and in the town's hospital where some were treated.
"We were moving along the road. We saw a car with all its doors open, parked. All of a sudden these men jumped out of the desert and started firing on us," said fighter Mohamed Khalil.
"As we sped away, two other cars followed and fired at us all the time. We just don't have the weapons to move forward," said Khalil, who was receiving treatment at the hospital for a bullet wound in his thigh.
Rebel fighter Mansour Rachid said the Gaddafi forces were spread out in the desert west of Ajdabiyah, a gateway to the rebel stronghold of Benghazi that has swung between government and rebel control in weeks of back-and-forth fighting.
"It is very hard to track them. They opened fire on us. We have two wounded and one guy was killed," said Rachid.
He pointed to blood on a rebel pick-up and shattered windows as evidence of the attack.
The rebels pushed the Gaddafi loyalists out of Ajdabiyah in a fierce battle on Sunday. Days of desert clashes followed.
On Thursday, rebel fighters vowed a new push on the oil town of Brega and by early afternoon the next day 40 rebel pick-ups with anti-aircraft cannon, machine guns and rockets had grouped near the western gate.
The sound of heavy bombardment boomed out of the desert, according to a Reuters witness. Rebels said the five explosions were the sound of NATO air strikes on Gaddafi's positions.
Men on trucks peered into the desert with binoculars.
Later the rebels appeared to lose enthusiasm for a new assault and some drove their trucks back into the town.
Morale seemed low among the small group of rebels waiting by the western gate for new orders.
"We can't advance beyond there. We just don't have the weapons," said Sharif Abdel Razak, pointing to a group of four or five rebel vehicles guarding the road beyond the western gate.
"We have no men beyond those vehicles up there," said fighter Fawzi Ramadan. "The only thing we can do is send people sometimes to see what is going on but we are not able to hold any ground beyond." (Writing by Tom Pfeiffer, Editing by Miral Fahmy and Andrew Heavens)